U.S. Pat. No. 4,475,905 discloses a dosage unit comprising a casing with an external thread over its entire length and a ring screwed on said thread. The ring is adjusted in relation to a measuring scale on the external surface of the casing, simultaneously serving as a retainer for a pin protruding through a slot of the casing, said pin being in solid connection with the piston of a syringe mounted in the casing.
U.S. Pat. No. 2,826,195 discloses a dosage unit for receiving a cartridge, the distal or front end of said cartridge being provided with a pierceable closure, through which one end of a double-pointed needle is pierced. After the cartridge has been inserted the needle is screwed to the distal end of the dosage unit one point passing through the adjacent closure of the cartridge.
Cartridges with different concentrations of insulin are used for the injection of insulin in dosage units of the above type. Usually, such cartridges contain 1.5 ml and the concentration of insulin herein can be 100 insulin units per ml, whereby the cartridge can contain 150 insulin units. In use a predetermined quantity is to be delivered by means of the dosage unit, preferably up to 40 insulin units per injection. By means of the dosage unit each cartridge can thus be used for several injections. Prior to each injection the dosage unit is adjusted to deliver exactly the amount of injectable preparation required in the particular case.